Daniel and Jorge Explain the UniverseListener Questions 64: Phase of the Universe, particle interactions and Universe-sized black holes!
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Hey Daniel, how many questions do we get about black holes?
Oh? Man? Maybe like half of all of our questions are about black holes.
Wow, So even after we've talked about it for so much, people still have questions.
You know. I think there's just like a never ending curiosity about black holes.
There's like a black hole of curiosity about black holes.
Maybe all of our answers are just going into a black hole somewhere.
Or maybe we're in a black hole if people can't listen to our answers, in.
Which case those people should just jump into the black hole with us and then they can hear all of our explanations.
That's why we could all be trapped in a black hole together.
Knowing the truth, but never able to escape.
But at least they can hang out with us.
Hi.
I'm Hooorhem made cartoonists and the author of Oliver's Great Big Universe.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I've pretty much accepted the fact that we may never see inside a black hole.
Well, I think that's definitely true, right, Like, if you're inside of a black hole, can you even see?
If you're inside a black hole, you can see things from outside the universe, And general relativity tells us we can never see inside a black hole. But you know, quantum mechanics opens a little door there we might one day be able to crack open. But maybe not. There might just be some secrets of the universe forever hidden from us.
But everything else we'll figure out.
Right, Wow, that's so optimistic. Everything else definitely, How to get a good night's sleep, definitely, sure. How to raise kids without concepts? Oh yeah, we'll figure all that stuff out, I'm sure.
Yeah. I mean, compared to black holes, that stuff is easy, right.
Compared to black holes, that stuff is actually hard because they're doesn't necessarily have to be an answer. At least with black holes, there's something in there, there is a truth. That's the thing I like about science questions as opposed to like philosophy or you know, moral questions, where there isn't always even an answer. At least science, you know there is a truth even if you don't know it. What if you can't know it, like, what if it's impossible to know? In which case isn't that the same as there not being an answer? Well, now you're asking a philosophical question to which there is no answer, which.
Are even harder questions than black holes?
Would it like to be a bat inside a black hole? Nobody will ever know?
What's it like to be a banana? That's an even harder question, more super subject.
Well, some fraction of you is bananas, so you could speak to that question. Wait what I'm saying. You are what you eat, and you eat a lot of bananas, so you are some fraction of banana.
But anyways, welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeart Radio.
In which we believe without justification, that the universe is understandable, that with our little minds we can somehow build models to explain how it all works out there, that our little mathematical tools can give us some insight into what's going on inside black holes, the early universe, the far future of the universe, and everything in between. We think that colliding questions and answers is like matter and antimatter annihilation, producing huge explosions of understanding. And we encourage you to think about the universe with us and come along for the journey.
That's right. We like to track here humanities. We're they attempt at trying to understand everything around us works and why it came to be the way it is, and to look into the darkest corners of the universe to ask questions and figure out what's going on even in black holes.
And while most of us don't get paid to think about these things about the universe. It is something that belongs to all of us and something that everybody can enjoy. We should all be thinking about the fundamental nature of our reality and wondering about it, trying to piece it together in our minds, and when something doesn't make sense, asking questions, why is it this way? How does this work? How does this fit with that thing? We'd love to encourage you to ask those questions, and specifically to ask them to us. Write to us to questions at Danielandjorghe dot com or straight to me to find my email address everywhere online. We will answer your questions. Everybody gets an answer.
That's right, because we believe everyone is part of science. Science is a group effort here with humanity because we all have questions about how everything works, why we're here, and what the true nature of the universe is.
Yes, science is democratic, is by the people and for the people. I'm not sure if it's of the people or not, or of the bananas, but science is about people. It's about people, some of it, yeah, sometimes sometimes yeah, there are scientific questions about people and encourage everybody to play a role because it's your curiosity that drives all of science forward, and that allows us to do research at the cutting edge and figure out the answers to fundamental questions about the universe. So please send us your questions. Sometimes I'll get a question and I think, oh, we should answer this one on the podcast, and I'll ask you to record yourself asking it so we can talk about it here on the pod. Yeah.
Sometimes we'd like to answer listener questions, and so today on the podcast, we'll be tackling listener questions Number sixty four.
It's a special Power of two edition.
Oh sixty four.
Yeah.
I think there are a lot of numbers that are the power of.
Yeah, but as you go up, there are fewer and fewer. We're not going to get to another one for a while.
Does that mean we ignore number thirty two we didn't commemorate.
Yes, unfortunately we missed those opportunities, but I didn't want to let another one slide by unmentioned.
Yes, we need to double our efforts here exactly. But I wonder if it even makes sense to keep counting these. You know, I think I've raced this before, but we seem to be doing these pretty often.
Yeah, We've been getting a lot more questions from listeners, and I feel bad about the backlog, and so we should be going through these. But it's helpful to have a number because then I can point people to them and let them know when their question is going to be answered. But if you prefer, we can give them a name. This can be Listener Questions Samantha or something. Bob Doug, Welcome to Listener Questions, Alfonso.
Well, we have some awesome questions here today, whether they're from Samantha, Bob or Alfonso, and they are about really interesting topics. We have some questions here about the beginning of the universe, about matter and antimatter, and of course about black holes. What percentage of our questions are about black holes, Daniel.
The ones that come in maybe like fifty percent, but I can't put them all on the pod.
Sounds like we need like a offshoot podcast just about black holes. But anyways, let's jump into it. Our first question comes from Dale, who lives in Washington.
Hi, Daniel and Jrage. My name is Dale and I live in and I have a question for you. You often say that at the beginning of our universe, physics was different when things were really dense and high, and that our universe had to cool off and dilute a bit for things to settle down to the way we see it now, all that in the future things will get so cool and alude that physics we see now won't work the same way. Not just the heat death of our universe, but possibly gravity or time or whatever just stops working as we understand it. Time to answer my question love the podcast.
All Right, an interesting question kind of about the beginning of the universe, but also about the end of the universe or the future of the universe.
Yeah, And I picked this question to talk about on the podcast because I think it raises a really important and kind of subtle issue about the physics that we're doing and what we know about how the universe works. Has to do with how things emerge from the fundamental rules of the universe, whether we know those fundamental rules, and whether the emergence stuff can change over time.
Yeah, it kind of raises the idea that maybe the rules of the universe can change, right, because the idea that scientists haves that maybe the rules of the universe have changed or they can change from the beginning of the universe.
Yeah, and that is probably confusing to people because they think, well, the universe follow some rules, and how could those rules change? So I think in your mind it's important to draw a distinction between like the fundamental laws of the universe sort of at the base level of reality. We don't know where that is or what that is, or what those laws are, but imagine that they exist as some sort of like foundational firmament, the basic bits of the universe, how they interact with each other. We think probably those don't change. Those were true always and they will always be true, But how those manifest themselves depends on sort of like the temperature and the conditions of the universe the same way that you experience, like in our everyday life. Take, for example, a glass of water. You know, you can describe the fluid dynamics of a glass of water when it's liquid, but those laws don't really apply anymore if you freeze it or if you turn it into steam. It's still the same basic rules describing like water molecules and how they interact. Those haven't changed, but the effective laws, what actually helps you describe what you're seeing, does change as the conditions change, and we think that probably is also true for particle physics. We think that the laws we have now are not the fundamental laws of the universe. They're more like the fluid dynamics or the crystal structures of water, or the ideal gas law for steam. They're an effective description of some emergent phenomena that has bubbled up from the fundamental laws.
Meaning they're sort of like f equals ma, Like it helps you throw baseball, it helps you launch a projectile, but it may not necessarily help you put too particles together.
Yeah, that's exactly right. E f equals ma isn't active law. You know, A more fundamental description of a baseball is thinking about the quantum mechanical wave function of all of those particles, and that's really hard to do. It's much more useful to talk about the emergent phenomena, the simplicity that somehow emerges from the chaos that's going on underneath. And the crucial thing to know is that that's really really hard to do. You can't always start from the tiny little bits and blobs toing and froing and derive the emergent phenomena. You mostly just have to observe them and say, oh, look, there is some simplification here.
So when you say that, do you have some effective laws in particle physics, what are those laws?
Like?
How would you describe the laws we have right now?
So we have laws at many, many different layers. You know, for example, we can talk about chemistry. Chemistry are effective laws. You want to talk about how hydrogen and oxygen come together to make water. Chemists have all sorts of rules about how that happens. Those are not the fundamental laws of the universe. They're effective laws. You want to drill down into atomic physics, talk about like the structure of the hydrogen atom. There are rules and laws there we can follow. Those are not the fundamental laws. Then you want to drill down into nuclear physics, we can do calculations. There's all these different layers at which you can do calculations. None of those are fundamental laws. Even the most basic level that we do understand quarks and leptons the standard model of particle physics. We sometimes describe those as the fundamental laws of the universe, but we're pretty sure they're not. We know, for example, as Dale mentions that they don't describe the very early universe that there's a moment before which our laws cannot describe, and so we know they have to be effective.
They're not fundamental, right, and I think the idea that these laws it can change or are different. It's not necessarily that they change, but it's more like they only apply to certain conditions, right, like ef equals. They may work for a baseball and a canonball, but doesn't work for little tiny particles, just like maybe your particle physics laws don't work under certain conditions, but they don't work maybe under extreme conditions, like maybe the kind we had at the beginning of the universe.
Yeah, the laws themselves don't change. The conditions change, and then which laws are relevant changes. Just like if you're floating in water, you're going to use a certain set of laws, and then if somebody boils that into steam, you're not going to use the fluid dynamics anymore. Now you're going to use your understanding of how gases work. And so the universe is changing because the universe is cooling. It started off very very hot and dense, in a state that we can't describe using our current laws. Because gravity and quantum mechanics were both important and we don't know how to unify them, And then it cooled to a place where we could do those calculations because mostly gravity and quantum mechanics don't intermingle and aren't both relevant. So we know how to do those calculations, and the universe has been cooling ever since. And Dale's question is, are we going to pass into some new phase where there are some new effective laws in the future of the universe, so that these effective laws aren't really relevant anymore.
Right, because like at the beginning of the universe, things are so hot and endstad I know we mentioned this in the podcast that the quantum fields were sort of different. They hadn't settled yet.
Yeah, there's sort of two different regimes there. One is before we can even really talk about quantum fields, where we're in a regime of quantum gravity, because quantum fields can't describe everything because they ignore the gravitational effects. So before that not even quantum fields are relevant. Then there's a period at the very beginning of the universe that we can describe using quantum fields. But the quantum fields have so much energy that doesn't really make sense to talk about like individual particles. The fields themselves are just frothing with energy. Then as the universe cools, particles start to be a useful thing to talk about, because the energy in the fields has spread out and matter has diluted enough that you have these individual pockets that are useful to talk about. So fields emerge first and then particles.
But isn't there a point set of where physicists talk about the Higgs field, sort of settling or finding a right spot.
Yeah, as the universe cools, all these fields, their energy dissipates, and a lot of them go to word zero, none of them actually to zero, and the Higgs field gets stuck at a particularly high value of potential energy, unlike a lot of the other fields, And that's the process of the whole universe cooling. But again, Dale's question is about, like the far future, are things going to change again so that we might need a new set of effective laws to describe what's going to happen.
Right, I guess the question is like, is the universe going to change or do you foresee the conditions of the universe changing enough so that our current laws don't even work.
Yeah, it's a good question. What we do think is the universe will keep expanding, which means it's going to keep cooling. And the current average temperature of the universe is about two point seven calvin. That's the temperature of the cosmic microwave background radiation that fills the universe. It's been red shifted down to two point seven calvin. So we're not that far from zero, right. We've gone a long way from very high temperature the early universe down to approaching zero. There's not much room left. But what we don't know is what the future holds.
But isn't it all sort a relative though?
Yeah, yeah, exactly, it's all sort of relative. We don't know what the future holds.
What seems like to us is a small change from zero to two point zero point seven or two point seven. It could be a big difference. We don't know, right, We don't know.
It could be very rich with interesting new physics on very different timescales, Like say, nothing fundamentally changes, maybe the Higgs field doesn't collapse and nothing else fundamentally changes. As we approach the heat death of the universe, things spread out and keep cooling. It could be that there are new emergent phenomena that come about, you know, the same particles we know about now moving very very slowly. The universe is very cold. There could be interesting things that happen instead of over microseconds or milliseconds or even seconds, over like centuries or millennia new emergent phenomena.
Wait, wait, are particles actually going to be moving slower?
If they're not?
Right?
Why do you say that?
Meaning like you might say that the temperature is getting lower, meaning like the average velocity of the particles per square cubic meter or something is getting smaller. But in the video particles, are they necessarily going to be going slower?
Well, the energy in the universe is decreasing as it expands, things do get red shifted. So, for example, photons lose energy right as the universe expands and they get stretched, they get red shifted.
So like let's say a natrina flying through space. I think we talked about this recently. If it's just flying through space and space is stretching, it's going to slow down.
So photons do not slow down, they lose energy. Particles with mass do get red shifted, though I know you objected to the use of the word red on that, and so they do lose energy. I think an intuitive way to think about it is think about expansion as the opposite of compression. If you compress things, they heat up, right, Why because you're confining them to a box, or something hits the edge of the box, you're turning it around, you're squeezing them. Expansion is the opposite process, and so that's why things cool down when they expand.
So particles do slow down, you're saying, as they fly through expanding space.
Yeah, and so you might imagine that in the future, if particles are all moving very slowly, there could still be really interesting things that happen. Like think about glaciers. Glaciers move super duper slowly, but there's interesting effects from glaciers right valleys and mountains and all sorts of geological effects that are super duper slow but that emerge over long periods of time. It could be that the universe in some future state is a cold soup that seems like it's not doing anything interesting in our scale, some new emergent laws could come about that are really fascinating and even lead to like complexity and life even over like much much longer time scales.
Hmmm, that would be interesting. Although it is a little bit slow. I wonder if something more dramatic could happen as things stretch out, like could maybe the Higgs field collapse again, or could maybe the electromagnetic field collapse suddenly.
It's certainly possible that the Higgs field collapses. Right, the Higgs field didn't cool like everything else the energy, and it got stuck because the Higgs field is different from the other fields. It has a different kind of potential energy. It's not straightforward for it to go down to zero. It sort of like gets stuck in a little valley on a hill instead of just rolling down the hill. It got stuck in this little valley and that's sort of embedded on the side of a hill, and it's not easy for it to go down to lower energy. But it's possible. We don't actually know how stable that little value is. It could get kicked out of there and then roll down the hill, in which case the universe would be in a very very different sort of effective phase because all these particles would lose their mass, and again the effective laws of physics would be different. The fundamental laws from the very very grounding of the universe wouldn't have changed, but the conditions of the universe will have changed, and so the effective laws might.
Could maybe in one of the other fields somehow collapse to or get stuck.
The other fields have a different structure, and so they already naturally gravitate towards zero. They're not at zero, and they can't be at zero because quantum mechanics prevents them from ever actually minimizing to zero. So the Higgs fields is the only one with what we call a vacuum expectation value because the structure of its potential energy is different. You know, these fields are weird. We're talking about like energy in the field. What does that mean? However, these fields can oscillate. They can vibrate the way string vibrates. Right, we have values of the fields, and the fields can have kinetic energy, which is the oscillation of the field. They can also have potential energy, which means like some configuration of the field has more energy than another configuration of the field, the way like pulling on a guitar string or a spring can give it energy just because of its configuration. And so these fields can store energy.
So it's possible for these fields to suddenly work in a different way.
Yeah, it is possible and also, as you've pointed out many times, we don't know that these fields actually describe fundamental things. You know, we used to think of the proton as having a field. We now know it actually is the field of various quarks, and the proton fields is just an effective description that sometimes works and sometimes doesn't. And so could be that the fields we're talking about are not even the fundamental fields of the universe. They're bubbling up from some tinier, little squiggly on fields that are the real description, and the conditions for the squigglyons could change, and the fields we're looking at could change. You know, we've tested to them under all sorts of conditions. We pretty confident that they work in the range of the temperature of the universe today and probably to the far future, because cold conditions are not hard to test in the lab. Really really hot conditions are much harder to test. But again we don't.
Know what about Dale's part of the question where you ask if maybe gravity or time can stop working or work in a different ways as possible as the universe expands.
It certainly is possible because we don't understand gravity or time, and these things are closely related to the expansion of the universe, and our current description of the expansion of the universe comes from general relativity, which tells us how it expands or contracts as you have matter density and radiation density and dark energy density. But most of that is dark energy, which is something we don't understand, and we also don't think general relativity is the correct description of the universe because it ignores quantum mechanics, and so you have a lot of possibility there for surprises. Dark energy could be very different from what we expect. You could do something different from what are now eve extrapolations suggest, and gravity could turn out to be very different from what we expect. You know, there could be additional dimensions of space and time and those could like unravel as time goes on. You never know.
All right, Well, it sounds like the answer for a dale is that, yes, it is possible that in the future, maybe physics will work differently. Maybe something will happen to the fields. The fields might snap or change, or gravity might unravel, as you say, And also maybe we'll get to see new kinds of physics because there'll be super extra colt conditions we have never maybe seen before in the universe exactly.
So eat blueberries and bananas, stay healthy so you can be around to see the loss of physics changing.
Do you want to see the laws of physics changing?
Absolutely?
Do you want to see the Higgs field collapse. I don't think we would get to see that experience that for very long.
No, we would not experience it for very long. But one of my dreams is to be around as humanity unravels some of these puzzles we talk about so many times, it'd be frustrating to pass on before we figure it out.
It sounds like eating a lot of chocolate. Maybe it's not going to help you.
I'm conflicted. I'm conflucted.
Some things may not be worth it. All right, Well, let's get to our next questions. We have a question here about matter and antimatter, and a question about black holes, and also about matter. So we'll get to those, But first, let's take a quick break.
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Right, we're answering listener questions here today, and our next question comes from James from Colorado.
Hi, Daniel and Jorge. This is James from Colorado. Thank you for your wonderful show and explanation. I still have a question I can't figure out. It has to do with annihilating antimatter and matter. When I think of two particles being in the same place, I thought that wasn't allowed, like a poly exclusion principle. But when I think of two particles as waitond, it feels like they're always touching. So how is it that antimatter and matter don't annihilate sometimes but do annihilate other times? How close does antimatter have to get to matter before it annihilates? I look forward to the explanation. It's chocolate and bananas.
Bye.
All right, interesting question, it's sort of a question and an anti question in itself. What sort of a statement but also a question.
Yeah, and he definitely wants to hear about chocolate and bananas. So he's even on brand for our jokes this episode.
Oh, he must be a faithful listener.
Thanks very much, James.
Oh, that's right, he said. He hopes it didn't. Well, was chocolate and bana? I feel like that's a challenge, all right, I'll bring the chocolate. Can white chocolate and dark chocolate exist at the same time.
If you annihilate dark and white chocolate, do you get bananas.
Or do you get plantains? You never know? They're quantum bananas.
They are.
Well, let's jump into it. Well, here's how I interpret the question. We've talked about before, how if you get anti matter together with matter, they annihilate and disappear. But then we've also talked about how like two particles can coexist in the same spot at the same time. So I think that's what's confusing James.
Yeah, exactly. And I think what's going on in James's mind is that he's imagining that matter and anti matter have to like touch or overlap in some physical way in order to annihilate. I think he's thinking about like two tiny grains of sand coming together and touching or overlapping and then turning into a flash of light. But instead we should think about matter antimatter annihilation.
Is you already failed Downny? You could have said a banana, but you went with a grain of sand.
An absolutely tiny banana.
I mean, that's such an easy fruit to pick. They're a little hanging fruit like bananas, but you went with the grains of sand.
Do you imagine that people think about particles as tiny bananas? I was thinking tiny particles, like tiny specks of matter.
We've always said they're not little balls. Maybe they're little banana shape particles.
So when you have these two tiny bananas, how do they actually annihilate? I think the useful thing is to remember that particle annihilation is just another kind of particle interaction. You know, when two particles come and bump against each other and change direction or something. They can change direction, they can also change what particles there are. So, for example, an electron and a positronic can come near each other and turn into a photon. So now you've changed the kind of particles there are. You can also have an electron just like emit a photon. So now you have changed to what kind of particles there are, And you can even wonder like, is the electron that came out of that the same as the electron that went into it? The point is just that antimatter annihilation is just another kind of interaction of particles. And for particles to interact, they don't have to actually touch or overlap each other. They do that at a distance using their fields.
But I guess what is it about Let's say an electron and a positron, which is an antimatter electron. What is it about them that makes them want to interact with each other? Like an electron and another electron don't interact with each other, do they? Or do they interact the same way? They just can't get them close enough together.
They definitely interact with each other. Absolutely, two electrons will push against each other. Right, where else does that repulsion come from? It comes from the interaction of those two electrons.
But not just pushing against each other, but sort of like transforming into something else.
Yeah, well, you know, you can ask the philosophical question of whether the electrons that came out of that interaction are the same as the electrons that went into the interaction. It's possible for those interactions to keep the same kinds of particles as they come out, but you know, it's a new momentum. It's a different direction. You could also say it's sort of like the incoming electrons disappear and you get new electrons coming out. But in the case of electrons and positrons annihilating and turning into a photon, it's much clearer that you don't have the same kinds of particles coming in as going out. But again, you don't need matter antimatter annihilation to do that. For example, you can have an electron come in and interact with a neutrino and give you a w boson. So now the electron and the neutrino are gone, but the electron and the neutrino are not matter antimatter pairs.
What would you say they annihilated each other.
You wouldn't say they annihilate, because that's only a special word we use for matter antimatter interactions. But the point I'm making is that that's really just a subset of particle interactions, and it's possible to change the kind of particles that exist without matter, antimatter, annihilations. It's like a special little subset. But to understand how it works, it's easiest to think about it in terms of the broader category. If just particles interacting with each other when they get near each other, which doesn't require them to actually overlap and touch.
Whoa wha whait whoa hold on?
Hold on.
You just got into word definitions there, and I have to force a little stop. Sure, so you're saying that you only use the word annihilation when it's matter and antimatter interacting with each other. But if two other particles interact and they totally disappear, just like the matter and antimatter, and they become something else, you don't call that annihilation. Why not?
I don't call that annihilation. That's just an interaction, you know.
But the same thing happens rights the exact same thing. You're just choosing the word annihilation for one ano the other.
Yeah, I don't actually like the word annihilation. I think of all these things as an interaction. I know that there's this word annihilation that's used to describe matter and antimatter, and so we can do that. But the point I'm making is that that's just a subset of broader category of interactions, some of which also include particles disappearing. And in fact, the point I was making earlier is you could argue every interaction involves the initial particles disappearing and new particles coming out. It's just in some of those the new particles are the same type and some of those they're not. But in every case it's sort of like the particles of theseus. You know, is it the same particle that came in and went out?
You're saying like all particle interactions are annihilation.
Kind of, I'm saying every time you have a particle interaction, you could view the final particles not the same as the initial particle. Sometimes it has some things in common, like oh, it's an electron also like the initial particle was, but it's also different in some ways. It's going in a new direction as a new energy. So yeah, the initial states disappear and the final states appear. Sometimes they have something in common, but they don't always have to.
But isn't there something special about matter and antimatter interactions or slash annihilation, which is that they release a lot of energy? So why do we think of those as releasing a lot of energy, but maybe not the others releasing a lot of energy.
They don't really release energy, they just transform it, you know, like when an electron and positron interact in a way to produce a photon, they've transformed matter into the energy of a photon, and we sometimes say into pure energy, but you know, there's no such thing as pure energy. Energy has to be in some form. In this case, it can be a photon or an electron and positron can also annihilate into a z boson, and so we talk about that because there is a flash of light if you do that. And so if you take, for example, a raisin and an anti raisin and they interact with each other and convert into a bunch of photons, that is a lot of energy because there is a lot of energy stored in the mass of that reason and anti raisin. So there's a lot of energy available to transform into photons. Which is why like matter antimatter engines would be very very powerful with very small amounts of fuel, just because there's so much energy stored in mass. Because equals mc squared C squared is a big number.
Well, I wonder if maybe the real explanation is that you know, when you have an electron and an anti electron, like, one thing that they can do is interact and turn into photons, which is going to be a lot. But maybe if I have an electron and another electron, that's not a possible interaction that can happen between the two of them.
Yeah, exactly. There's a lot of rules in particle physics about what can happen and what can't happen, and so that's why, for example, you can't have an electron and a proton turn into a photon, right because there's a rule against that. There's actually two different rules against that. The universe says you can't just delete electrons. It keeps track of the number of electrons, and so you can't just delete an electron from the universe. It also keeps track of the number of baryons. A proton is a kind of baryon, so you can't just delete a baryon from the universe. So that's why you can do electron positron annihilation because a positron counts as a negative electron. So you can destroy an electron if you also destroy it anti electron.
But I think maybe James's question was more, how does this annihilation and interaction interact with what I think we've talked but before, which is maybe the poly exclusion principle, which is, you know, the certain rules that say you can't have two particles super close to each other they repel each other kind of naturally, like in a neutron star for example.
Yeah, and that's a good question. And remember the poly exclusion principle applies to identical particles. So two electrons cannot be in the same state at the same time.
Why not?
Why can they not be in the same state at the same time. Yeah, particles that have spin one half follow certain quantum rules, and if you try to write down a solution to the rules of quantum mechanics for two spin one half particles in exactly the same state, the math just doesn't work. It's incompatible. The only way to satisfy the equations is for that state to not exist. So mathematically it's just incoherent, like there are no solutions to those equations. We actually answer this on the podcast in some more detail another time, talking about the spin statistics theorem, which is what determines this. So particles of spin one or spin zero behave differently in quantum mechanics, and they can exists on top of each other and have solutions to the equations. But you can't do that with spin one and half particles like electrons. You can with photons. As many photons as you like can lie on top of each other.
So can an electron and an anti electron be in the same spot at the same time.
They can be in the same spot at the same time because they're not identical particles, right, there's already something to distinguish them. The point of the poly exclusion principle is something has to distinguish them. You can have two electrons at different energy levels, or at different locations, or different something else's different spins, or you can have two different particles. An electron and a positron can be on top of each other and be identical in every other way. The poly exclusion principle does not prevent that.
So I guess that's basically the answer for James, which is that the exclusion principle only applies to particles that are the same. Yeah, identical matter and antimatter are not the same.
They are not the same. Yeah.
In fact, they're sort of anti each other.
Yeah, they're also sort of very closely connected.
You know.
The electron's closest cousin is the positron. It's just like another thing that the same field can do. There's only one field that makes the electron and the positron. It's just two different ways that it can wiggle.
What but they have opposite charge, So the same field can make the same wiggle, but they have different charge.
Yeah, exactly, there's no positron field in the universe. It's just an electron field. It can wiggle like an electron, or can wiggle like a positron. It's two different wiggles the same field can do. It's like the way you can do more than one dance, right, I hope, I assume. I don't know, never seen you dance.
Yeah, that's a shame.
It might annihilate my eyeballs. I don't know.
Yeah, or I mean just interact with your eye bed you go.
James also asks how close do they have to get before they annihilate? Remember that these things happen via fields and particles never have to be on top of each other in order to interact or to annihilate. So an electron and a positron can annihilate with each other turned into a photon at some distance. In fact, it always happens some distance because in our theory, these particles are point particles, and so they really have no size that we can determine.
Well, I mean, there's something a little bit more to it, though, right, because like an electron and an anti electron, they have opposite charges, so they actually attract each other.
Right, absolutely, they do. They will pull towards each other. If you have an electron and a positron alone in the universe, eventually they will come together and annihilate.
And so when they're really close to each other, they're going to be pulling each other even closer, which then raises even the probability that they'll annihilate and interact.
Exactly, and the word you used was very precise. There probabilities. These things are quantum mechanical, and so there's always a probability for these things to happen. And as the electron and positron get closer and closer, the probability of turning into a photon increases, But it's always a probability. It's always the universe rolling a die, or if there's no observation maintaining all those probabilities in parallel in superposition.
Right, So, I wonder if it's possible for an elect an anti lecron to attract each other, pull each other in, and even though it's improbable that have them not interact until they're right on top of each other. Is that possible?
It's possible, except I'm not sure what you mean by riot on top of each other. If we're thinking about.
Right on top of each other occupying the exact same space.
Yeah, well, that depends on whether space has infinite resolution and whether electrons are infinitely small. If so, then it might be impossible for them to be literally in the same location. Two infinitely precise numbers can never be exactly the same.
Well, well, there's sort of point particles right.
In our theory, we suspect they're probably not. They actually do have some extent and substructure even but in our theory they are currently point particles.
Yeah, so could they exist in the same point.
It's like asking if two infinitely long strings of numbers are the same, right, can they ever be exactly the same two physical.
Things they do? The answers yes, right.
You're asking a lot of philosophy questions here on the pod today.
I do have a PhD.
Man, Exactly, you're a doctor of philosophy, and it shows.
I can't cure your philosophy though, or prescribe any medication for it. I can only record a podcast.
Well, in order to satisfy James, how much chocolate and bananas does it take to cure somebody of philosophy?
Well, if you eat enough chocolate, you can definitely be cured of many things, including living, including having a working hard. But yeah, let's try to bring it back to chocolates and bananas. So I think what you're saying is that this rule in the universe that says that two things can be in the same spot at the same time only applies to things that are the same. So you can't have two bananas at the same insane spot, or two chocolate shaped bananas in the same spot. But it doesn't apply to things very different. So you can have a banana on top of a chocolate.
Yeah, and only two spin one half particles. Right, So photons, for example, can be in exactly the same spot even if they have the same energy, et cetera. There's no limitation there. They're bosons.
Wait, what what else is like light? Does only light have none spin one half?
No, all the force particles have inteed your spin. The Higgs boson has spin zero, The Z and the W are spin one. The graviton, if it exists, is spin two. So all the force particles have into your spin and all the matter particles have half into your spin spin one half.
All right, So then the answer is if the rule applies to you, it only applies if you're the same part Yeah, thanks for the same kind of snack. Yeah, all right, Well, thanks James for that question. Let's get to our last question, and it's about kind of all the things black holes matter, the universe and what's inside. So let's get to it. But first, let's take another quick break.
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Right as your listener questions. And our last question here is about, of course, black holes.
This is a question about the size of a black hole. So if you add up all of the matter so dark matter and matter matter, real matter in the universe, and apply the schwartz Child's equation, how big would the resulting black hole be?
All Right? Basically I think the question here is what's the biggest black hole you can make?
Yeah, instead of asking like, is our universe a black hole? If not, why not? It's a really interesting question and it comes down to some pretty simple mathematics that predicts when you get a black hole and when you don't, which is what Rebecca's referring to when she mentions the short styled equation.
Right, right, that's the equation that tells you, like, if you condense a matter, stuff, and energy into a certain sphere, then you get a black hole. If you don't, you don't get a black hole.
Yeah, exactly. And the equation is very simple. It says, if you have a certain amount of mass, then if you contain all that mass in a radius of less than two times the gravitational constant times the mass divided by the speed of light squared, then that's a black hole. So it's called the short stiled radius.
Well, it's weird, how It's so simple, isn't it.
It's amazing. Yeah, it's really kind of beautiful.
So it's just a mass time, there's some constant divided by the speed of light.
Yeah, and it's linear in mass, which is really interesting, right, which means twice as much mass means the radius grows by two. Right, ten times as much mass, the radius grows by ten, Which is why we talked about one time on the podcast how black holes that are larger technically are lower density because if the mass doubles, the radius doubles, which means a volume octoples.
So I guess Rebecca's question here then, is what if you took everything that we know about in the universe, I guess everything in the observable universe, and you squeeze it down into a black hole. What's the maximum size of this black hole can be?
Yeah, and the answer is going to be sort of weird and shocking, because as black holes get larger, their radius gets larger very quickly.
Well, first of all, how much stuff and energy is there in the universe? Do we have a number for that?
Yeah, So we can calculate that for the observable universe, for the part of the universe that we can see. So the observable universe is about forty six billion light years across. And we know a lot about the density of energy in the universe because we've measured the curvature of it, and we can calculate the massive galaxies and stars and dark mass and even dark energy, and that comes out to be a pretty small number. It's like ten to the minus thirty grams per cubic centimeter. But that lets us calculate the total effective mass of the universe.
And when you say mass, you also mean energy, right, Like you're also counting all the light and are you also counting the dark matter and dark energy?
Yes, all the energy in the universe, including dark matter and dark energy. We can treat it as if it was just mass. Equivalent mass of that equals mc square. Take the energy acts as if it was mass.
But I feel like, you know, the mass of stars and planets and rocks and even dark matter. You could technically squeeze that down if you move it. But could you move or squeeze the dark energy of the universe.
Turns out you're not going to need to. What do you mean? So wait for it. I'll walk through the calculation the total mass contained in the observable universe is something like ten to the fifty seven grams, which is huge. But the Schwartzild radius for that is four hundred and seventy five billion lights years. That's pretty weird. That says, if you have a bunch of stuff, which is the mass of the observable universe, you only need to squeeze it down into a size much much bigger than the observable universe before it becomes a black hole.
Wait what that means to someone outside of our observable universe. We are a black hole.
That's the interpretation on the face of it, right, That's what it seems like. There's important coyots in that calculation. We're not sure that the Schwartz out of radius calculation applies in this scenario.
Oh wait, let me see if I get this raight. This so you're saying the density of energy and mass in the observable universe is higher than it is in a black hole.
In a black hole of the radius of the observable universe. Remember, the density of black holes gets very very low as they get big because the radius grows with the mass, but the volume goes as mass cubed. Right, So as black holes get very very large, their density actually becomes very very low. And so even though our observable universe is very low energy density averaged over all the vast reaches of space, it's actually larger energy density than a black hole of that radius.
But does that mean that, Like, let's say I was a giant you know, I don't know if you know the comic book character Galactus. Like, let's say you're being that's bigger than the observable universe, and I held the observable universe in my hand, would I just be looking at a black hole?
It depends on a couple of things, right, So if the rest of the universe is empty, and the observable universe has no electric charge and no spin, then yes, if you took as much stuff as there is in the observable universe and crammed it into the radius of the observable universe, it would be a black hole. That doesn't mean that our universe is a black hole, because we don't know what's outside of it. This calculation, the Schwartzel's radius calculation, it's a simple, beautiful equation because it's making a bunch of important approximations that might not apply to our universe. Number one, it assumes that everything has no spin, that everything has no electric charge, right, and that there's nothing outside of it. When Schwartzoul did his calculation, like how do you make a black hole? He did it in a very simplified situation. He imagined an empty universe with nothing else in it, and then a blob of matter, and he calculated how much you would have to squeeze that down to make a black hole.
How o there being stuff elsewhere affect whether or not you make a black hole or not?
Well, the general relativity stuff is a little bit complicated to think about. To gain some intuition, we can think about a sort of Newtonian point of view, like just think about gravity as a force. You know, if you have a universe filled with stuff, are you going to get black holes? Even if the energy dency is really really high, even if you're exceeding the swartzyle redius, will you get black holes? No, because everything is tugging on stuff, right, Having stuff outside will prevent anything from collapsing and falling in. And so there is gravity from stuff outside that affects what's going to happen inside, and so what you really need in order to have a black hole is a region of high energy density surrounded by a region of low energy density. That's why, for example, in the early universe, when everything was filled with energy, it didn't just collapse into one big black hole because it was mostly uniform. And so that's why it's crucial part of that calculation that the stuff is surrounded by an empty universe, so it can collapse into a black hole.
I think I'm starting to understand here. It's sort of like that analogy that they're use in physics class a lot about gravity, which is like a giant rubber sheet, and if you place a planet or a bowling ball, it creates an indentation, and that's sort of like gravity. I think what you're saying is that you basically need a flat sheet of rubber in order to poke a hole in it, or to press down into it enough to create a black hole. But if, like you know, you put a bazillion bowling balls into this rubber sheet, then not one ball is going to create enough of an indentation to make a black hole. The whole basic rubber sheet just bows down.
Yeah, there are many flaws in the rubber sheet analogy which can be misleading, but in some cases it can be useful. And here, yeah, think of a black hole not as some absolute stretching of the sheet, but a relative stretching right a place where things are stretched much more than the surroundings. And so if you put an InFine number of bowling balls, you get no black holes. Rather than an infinite number of black holes, you need one bowling ball to stretch the sheet relative to the surroundings.
You need like a mega bowling ball amidst all of the other bowling bulls.
Exactly. So, if you're the Galacticus giant and the galactus, sorry, if you're the Galactus giant.
We don't want to get hate mail from marble things.
If the only mask in the universe is inside the observable universe, then yes, it satisfies to wart Style's condition, and it is a black hole. But if the observable universe is just one scoop of a potentially much larger, maybe infinite universe, and like you know, fifty billion light years over there's just as much stuff as there is here, then no, none of it's going to be a black hole. And so It really depends what's going on outside the observable universe whether our universe is a black hole or not.
Right, like, the observable universe is a bowling ball, and if the rest of the universe is just a flatsheet of rubber with nothing in it, then yes, we are living inside of a black hole. But if the rest of the universe is just more bowling balls, then we're not a black hole. Yeah, exactly does that mean that if you're inside of a black hole you can things sort of look normal?
We really just don't know. It could be that inside a black hole that it's very very low density, that a lot of interesting things can still happen. It can take time for that to collapse into a singularity. Another crucial thing about short Sid's calculation is that he was not taking into account and expanding universe right in his calculation. He did not have dark energy, and dark energy completely changes the general relativity of it. So an expanding universe also violates short Sid's calculation. And we don't know how to calculate what happens to masses in an expanding universe, whether they make black holes or not. That equations are too complicated, So I don't know the answer to that question.
But I feel like maybe the takeaway here is that we could be living in a black hole and not know it.
We could be living in a black hole and not know it. To me, I think it's unlikely because it would require the rest of the universe to somehow magically have no stuff in it.
That's the kind of thing someone living in a black hole would think to be, like, how can the rest of the universe not be a blood the same as here? You know, it's like the whole fish in a fishbole analogy. You're like, you're a fish in a fishball. Even less, think the whole universe is made out of water.
Yeah, it's possible. And if the rest of the universe is vacuum, then there's nobody in that vacuum wondering why they're in a vacuum. There are only people in not vacuum thinking the rest of the universe is not vacuum. So you're right, and we don't know.
But it doesn't have to be a vacuum, does it. It could just be like empty space or less dense space.
Yeah, exactly, that's what I mean. I don't mean no space, I mean empty space by the vacuum. But we also again don't know how to calculate what happened to very dense mass in an expanding universe, So the expansion of the universe might prevent it from turning into a black hole in that steo. Also, you know, our prediction for what happens to our cosmos currently is that all the glack the clusters collapse into black holes, which are then separated by dark energy. And so it could be that super duper huge black holes in expanding space don't have a singularity to have a bunch of singularities inside of them that are separated by expanding space. Maybe we just don't know how to calculate those things in general relativity, so we don't even know what would happen I.
See, and then what would happen to the shortshout equation if you didn't take into account chocolate and bananas, would it still be the same word?
Depends on the fraction of the universe that is chocolate and bananas, which is decreasing as we go on bull in time because of our contributions.
That's right, that's right, because we're eating it and turning into a different kind of dark matter. All right, Well, I think that's the answer for Rebecca, which is a super interesting question, which is that, Yeah, if you look at the density of the universe, we should be living in a black hole. But who knows. It depends on what is outside of the observable universe.
Yeah, that's right. And remember that a lot of the calculations we do in general relativity are for very specific, simplified situations and cannot be applied to more realistic situations.
Wait, wait, do you mean general relativity? It doesn't apply to the general case.
It applies to the general case, but we don't know how to solve it in the general case. Only a few solutions have ever been found for very highly simplified situations like a universe filled equally smooth with stuff, or an empty universe, or a dot of matter in the universe. We can't even solve it for like our solar system. So it's very complicated, and so be very careful applying simplified solutions to more general cases.
Man, that is just bananas.
Go have some chocolate and feel better.
Just trying to bring it back for James. I'm just trying to satisfy James's request here, all right, Well, those are three awesome questions. Thank you to our question askers. I think another great reminder of how there are things in this universe that we don't know and may never know. Will the universe change its rule? Are we living in a black hole?
Will you die first if you eat too many bananas or too much chocolate?
Or if you annihilate the dark chocolate and bananas? Is that going to kill you faster? Probably?
Let's find out that's.
Fine, No, it's not fine enough. Or you find out and then you will report it to the podcast. Sounds good posthumously. I'll do my homework, all right, Well, thanks again everyone for asking these questions. You hope you enjoyed that. Thanks for joining us. See you next time.
For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, dis org, Instant, and now TikTok. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth You're probably not thinking about the environmental impact, but the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is US dairy tackling greenhouse gases? Many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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